The present invention relates to a scan control method and an X-ray CT (Computed Tomography) apparatus, and more specifically to a scan control method for an X-ray CT apparatus, for helically scanning a subject with a contrast agent injected therein, and an X-ray CT apparatus which helically scans a subject with a contrast agent injected therein. Alternatively, the present invention relates to an applied technology for a variable helical scan in an X-ray CT apparatus.
In an X-ray CT apparatus which helically scans a subject with a contrast agent injected therein, a helical scan is performed which is synchronized with the attainment of a bloodstream contrasted with a contrast agent to a region of interest in a monitor phase. In such a case, a scan with a helical scan velocity as constant is carried out after the start of the helical scan (refer to, for example, the following patent document 1).
[Patent Document 1] Japanese Unexamined Patent Publication No. Hei 09(1997)-327454 (fourth to fifth pages and FIGS. 7 through 9).
In order to suitably perform contrast photography by the scan with the helical scan velocity as constant, there is a need to make a bloodstream contrasted with a contrast agent in advance. Therefore, the contrast agent is apt to often use so that a burden on a patient increases. With this view, there is a need to reduce the amount of the contrast agent as much as possible.
In an X-ray CT apparatus which makes use of a multi-row X-ray detector or a plane X-ray detector, the velocity of a helical scan is on the increase with an increase in helical pitch due to three-dimensional image reconstruction and enlargement of a detector width in a z-axis (body-axis) direction. The velocity of the helical scan might be faster than the velocity of the bloodstream contrasted with the contrast agent. Therefore, there has been a demand for control of the helical scan velocity.